1. Field of the Invention
The present invention relates to an image pickup apparatus and a method therefor. In particular, the invention relates to an image pickup apparatus and a method therefor suitable for use in a camera with variable ISO (International Organization for Standardization) sensitivity setting and applicable to an electronic still camera device, image input device, movie camera, mobile phone, etc.
2. Description of the Background Art
Conventionally, an imaging apparatus such as an electronic camera is configured to shoot with a built-in slave and flash unit under a dark condition or to accommodate an external flash unit detachably mounted on the hot shoe of the camera, thereby allowing the camera to clearly capture shots even under a dark condition, e.g., at night. For example, Japanese patent laid-open publication No. 2005-184508 discloses a method for pre-flashing before main flashing, when taking a photograph of a person standing with his or her back to the sky at night, to radiate the light toward his or her face to be shot and detect the face so as to determine the area of the object in a picture to be shot, thereby better controlling the flashing.
Further, another method has also been employed for allowing a photographer to adjust the ISO sensitivity or speed setting on a camera to the state of so-called “ISO Auto” in which the ISO sensitivity is automatically adjusted in response to the output signal of the photo-metering circuit or to manually set the ISO sensitivity to its higher level in order to be able to photograph under a dark lighting condition. When the subject of principal interest in the central portion of a scene to be photographed is relatively darker, the ISO sensitivity is set to its higher level.
In some cases, if the ISO sensitivity setting is switched to “ISO Auto”, allowing a photographer to take a photograph of a subject such as a person standing with his or her back to the sky at night, the exposure control is interfered by a brighter object such as a street lamp so that the photograph of the subject will be underexposed. This is because the photograph is taken almost against the light causing the image of the subject to become dark.